Properly validate arguments within VCert playbook

[cdmadrigal]

BUSINESS PROBLEM
N/A

PROPOSED SOLUTION
Any arguments that are entered within the VCert playbook should be validated to make sure they are allowed in that location. For example, if you set sanDNS within the subject: block, VCert will run properly without an error. This should throw an error because sanDNS does not belong in the subject: block.

This would make it easier for new users for VCert to know when they have misconfigured the playbook by putting arguments where they shouldn't be.

CURRENT ALTERNATIVES
Look at examples and figure out where the arguments should be placed. Makes troubleshooting difficult for new users.